The invention relates to a pressure-fluid-operated power unit producing a rotating motion for positioning valves, or similar actuators, into a desired position, the rotating motion of the actuator being a multiple of about 90xc2x0, the power unit comprising a cylindrical casing, a first end flange and a second end flange being provided at the ends of the casing, an annular cylinder space, and at least two pairs of pistons, the pistons being movable with respect to each other and substantially of the same shape and size as the cross-section of the cylinder space, the first pistons in each piston pair being movably arranged with respect to the cylinder space, the first pistons rotating about its axis so that the first pistons can move in the cylinder space in the direction of its circumference; and the second pistons of the piston pair adjacent to the second end flange being immovably arranged with respect to the second end flange of the cylinder space or the casing of the cylinder space; and a transmission shaft arranged to rotate about the axis of the cylinder space with said first pistons for transmitting power for the positioning of the actuator.
Various actuators having a control member the position of which is rotatably adjustable and an adjusting range which is a multiple of substantially 90xc2x0 are widely known. Such actuators include various valves, for example. Often these actuators are set to a desired position using power units which are typically pressure-fluid-operated.
In prior art pressure-fluid-operated power units the energy of the pressure fluid is usually converted to a motion of a usually linearly moving piston or similar member, the motion being further converted to a rotating motion for example by applying a gear rack and gearwheel, a lever or other similar transmission means. Power units are therefore often complicated in structure, and their manufacturing and maintenance is expensive and time-consuming. Such power units naturally require a fairly large space, which makes them difficult to position in connection with actuators. The power of a power unit is also relatively low with respect to the space it requires. Furthermore, complicated power transmission solutions cause looseness and tolerance which impede the accurate adjustment of the actuator and which become worse during the service life of the actuator.
An object of the present invention is to provide a power unit where the above drawbacks are eliminated.
The power unit of the invention is characterized in that the power unit comprises at least one additional annular cylinder space arranged co-axially with the cylinder space between the first end flange and the second end flange; that the cylinder space adjacent to the additional cylinder space and/or additional cylinder spaces are separated from each other by an intermediate flange which is arranged to move with respect to the cylinder space and the additional cylinder spaces and the and the transmission shaft, the flange rotating about their axis; that the additional cylinder space is provided with at least two pairs of additional pistons, the additional pistons of which are substantially of the same shape and size as the cross-section of the additional cylinder space; that the second additional pistons of the additional piston pairs arranged to the additional cylinder space limited by the second end flange are immovably fastened with regard to the second end flange or the casing of the cylinder space, the second additional pistons arranged to other additional cylinder spaces and the second pistons of the cylinder space being fastened to the intermediate flange, on the opposite side of which are fastened the first additional pistons of the adjacent additional cylinder space; that additional piston pairs arranged into one and the same additional cylinder space can move with respect to each other in the direction of the circumference of the additional cylinder space; and pressure fluid conduits for leading pressure fluid into and out of the spaces between the additional pistons.
An essential idea of the invention is that the power unit comprises an annular cylinder space and at least two pairs of pistons arranged into said cylinder space and moving with respect to each other, a first piston in the piston pairs being arranged to rotate about the axis of the cylinder space and a second piston being immovably arranged with respect to at least one end flange of the cylinder space or the casing of the cylinder space; and pressure fluid conduits for leading pressure fluid into and out of the spaces between the pistons. A further idea of the invention is that the power unit comprises a transmission shaft for transmitting the motion of the pistons that are arranged to rotate with respect to the cylinder space to the control members of an actuator, for setting the position of the control members.
In addition, an idea of a preferred embodiment is that an additional cylinder space is provided co-axially with the cylinder space; that the cylinder space and the additional cylinder space are separated from each other by an intermediate flange which is arranged to rotate about the shaft of the cylinder space and the power transmission means, second pistons of the pistons pairs being immovably arranged on the cylinder side of the flange; and that the additional cylinder space is provided with at least two additional piston pairs, a first additional piston of which is immovably arranged on the additional cylinder space side of the intermediate flange, a second additional piston being immovably arranged to the flange closing the additional cylinder space in such a way that the additional pistons can rotate in the direction of the circumference of the additional cylinder space, whereby the transmission shaft can be rotated with respect to the flange closing the additional cylinder space by feeding pressure fluid into both the cylinder space and the additional cylinder space, thereby allowing the maximum angle of rotation of the transmission shaft to be increased.
A second preferred embodiment is based on the idea that the transmission shaft is arranged directly to the shaft of the power unit""s actuator, the arrangement between the power unit and the actuator being as simple as possible. A third preferred embodiment is based on the idea that the pressure fluid in the power unit is a water-based liquid, or steam. The pressure fluid can also be a process liquid.
An advantage of the invention is that the power unit is small with respect to its control power, therefore the unit can be placed even into a narrow space. A further advantage is that the structure of the power unit is simple, whereby its manufacturing and maintenance costs are low. The power unit produces a rotating motion directly, therefore any power transmission means complicating its structure are not needed between the power unit and the actuator. The number of the additional cylinder spaces is easy to select, whereby the greatest possible rotating motion of the power unit is simple to increase. Yet another advantage is that in the power unit of the invention, either water or an aqueous solution can be used as pressure fluid, the actuator thus being extremely safe, environmentally friendly and economical to use.